Shape-distorting tooling system for curing composite parts

ABSTRACT

A tooling system may include a cure tool and a biasing element. The cure tool may have a cure tool coefficient of thermal expansion (CTE) and may be configured for curing a composite article formed of two or more components having dissimilar component CTEs. The biasing element may be fixedly attached to the cure tool and has a biasing element CTE that may be different than the cure tool CTE. The biasing element may be configured such that a combination of the cure tool CTE and the biasing element CTE causes a heat-up displacement in the cure tool when heated and the composite article is cured in a distorted shape. When the cured composite article is cooled, the cured composite article may substantially assume an as-designed shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of and claimspriority to pending U.S. application Ser. No. 13/649,013 filed on Oct.10, 2012, and entitled SHAPE-DISTORTING TOOLING SYSTEM AND METHOD FORCURING COMPOSITE PARTS, the entire contents of which is expresslyincorporated by reference herein.

FIELD

The present disclosure relates generally to composites manufacturingand, more particularly, to controlling thermally-induced shapedistortion during the curing of composite articles.

BACKGROUND

The main rotor blades of many helicopters and other rotorcraft arefabricated from composite materials due to the superior stiffness andstrength properties and corrosion resistance of composites. Such highstiffness and strength properties provide an increased fatigue life forthe rotor blades in the high-vibration environment of a helicopter. Inaddition, composite materials provide a means for tailoring the mass andstiffness characteristics at different locations along the span of arotor blade to optimize the aeroelastic performance of the rotor blade.

In this regard, a main rotor blade may be constructed with differenttypes of materials positioned at different locations within the airfoilshape of the rotor blade to achieve specific structural stiffness andbalance characteristics. Different materials may also be positioned atspecific locations along the airfoil shape or material thicknesses maybe varied along the length to provide operational durability for therotor blade. For example, a metallic skin may be included on the leadingedge of a composite spar of a rotor blade to provide erosion durabilityfor the rotor blade.

The use of different types of materials for different components withinthe rotor blade may result in imbalances in the thermal expansioncharacteristics of the dissimilar materials. For example, the metallicskin may have a coefficient of thermal expansion that is higher that thecoefficient of thermal expansion of the composite spar. The metallicskin may be adhesively bonded to the composite spar at an elevated curetemperature inside a cure tool. The differing coefficients of thermalexpansion of the metallic skin and composite spar may result in themetallic skin shrinking along a lengthwise direction to a greater extentthan the shrinkage of the composite spar. Because of cross-linking thatoccurs during adhesive cure, a rigid bondline is formed between themetallic skin and composite spar. The rigid bondline results in stressbuildup between the metallic skin and the composite spar upon cool downfrom the cure temperature which may result in shape distortion such asbowing in the cured spar assembly.

Conventional approaches for minimizing shape distortion during themanufacturing of rotor blades include the use of cure tools that aredesigned to be highly rigid and/or which have a low coefficient ofthermal expansion to minimize distortion during the cure cycle in anattempt to maintain the rotor blade in a desired (e.g., straight) shape.Complex holding features may also be incorporated into sub-assemblyparts and subsequent cure tools in an attempt to lock the rotor bladecomponents into a desired straight condition. Unfortunately,conventional approaches fail to adequately address the shape distortion(e.g., bowing) that occurs in a composite rotor blade as a result of theimbalance in the dissimilar materials with regard to thermal contractionafter cure. Such shape distortion in cured composite subassemblies maypresent challenges in fitting the cured subassemblies into subsequentcure tools and compromise the integrity of the final part.

As can be seen, there exists a need in the art for a system and methodfor minimizing or eliminating shape distortion in cured compositearticles comprised of dissimilar materials.

SUMMARY

The above-noted needs associated with thermally-induced shape distortionin composite structure are specifically addressed and alleviated by thepresent disclosure which provides a tooling system having a cure tooland a biasing element. The cure tool has a cure tool coefficient ofthermal expansion (CTE) and may be configured for curing a compositearticle formed of two or more components having dissimilar componentCTEs. The biasing element may be fixedly attached to the cure tool andhas a biasing element CTE that may be different than the cure tool CTE.The biasing element may be configured such that a combination of thecure tool CTE and the biasing element CTE causes a heat-up displacementinto a distorted shape of the cure tool when heated. The compositearticle may be cured in the distorted shape such that when cooled, thecured composite article may substantially assume an as-designed shape.

In a further embodiment, disclosed is a tooling system, comprising acure tool having a cure tool coefficient of thermal expansion (CTE) andwhich may be configured for curing a composite article formed of two ormore components having dissimilar component CTEs. The tooling system mayfurther include a biasing element that may be fixedly attached to thecure tool. The biasing element may have a biasing element CTE that isdifferent than the cure tool CTE. The biasing element may be configuredsuch that a combination of the cure tool CTE and the biasing element CTEcauses a heat-up displacement in the cure tool when heated to a curetemperature and the composite article is cured in a distorted shape suchthat when cooled to ambient temperature, the cured composite articlesubstantially assumes an as-designed shape when unrestrained. Thebiasing element may be fixedly attached to the cure tool at a locationon the cure tool such that the heat-up displacement is substantiallyopposite in direction to a cool-down displacement of a cured compositearticle cured on a non-biasing cure tool.

Also disclosed is a method of manufacturing a composite article. Themethod may include providing a cure tool having a biasing elementfixedly attached thereto. The cure tool has a cure tool coefficient ofthermal expansion (CTE). The biasing element may have a biasing elementCTE that is different than the cure tool CTE. The method may includeloading a composite article on the cure tool. The composite article maybe comprised of components having dissimilar component CTEs. The methodmay include heating the composite article and the cure tool to a curingtemperature. The method may additionally include distorting the curetool into a distorted shape in response to elevating the temperature ofthe cure tool to the curing temperature due to the difference in thecure tool CTE and the biasing element CTE. The method may also includecuring the composite article in the distorted shape, and then coolingthe cured composite article such that the cured composite articlechanges shape from the distorted shape to an as-designed shape.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawingsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become moreapparent upon reference to the drawings wherein like numbers refer tolike parts throughout and wherein:

FIG. 1 is a perspective view of a spar assembly of a rotor bladecomprising a pre-cured composite D-spar and a metallic erosion stripbonded to the D-spar and wherein the D-spar and the metallic erosionstrip may have dissimilar coefficients of thermal expansion (CTEs);

FIG. 2 is a perspective view of an embodiment of a tooling system as maybe implemented for bonding the metallic strip to the D-spar leading edgeto form the spar assembly illustrated in FIG. 1;

FIG. 3 is a side view of the tooling system illustrating the cure toolsupported on a support frame and further illustrating a biasing elementfixedly attached to a lower side of a tool base of the cure tool andwherein the biasing element coefficient of thermal expansion (CTE) isdifferent than the cure tool CTE;

FIG. 4 is a cross-sectional view of the tooling system taken along line4 of FIG. 3 and illustrating the biasing element attached to the lowerside of the tool base and further illustrating the metallic erosionstrip and the composite D-spar loaded within a cure tool cavity definedby the tool base and a tool cap

FIG. 5 is a perspective view of the cure tool having a tool cap mountedto an upper side of the tool base and the biasing element fixedlyattached to the lower side of the tool base;

FIG. 6 is an exploded perspective view of the cure tool, the biasingelement, and the spar assembly and illustrating the metallic erosionstrip and the D-spar that may be loaded into the cure tool;

FIG. 7 is an exploded cross-sectional view of the tooling systemincluding the tool cap, the cure tool, the biasing element, and furtherillustrating the spar assembly that may be bonded to the D-spar usingthe cure tool;

FIG. 8 is an exploded side view of a non-biasing tooling system thatlacks a biasing element;

FIG. 8A is an exploded cross-sectional view of the non-biasing toolingsystem including a tool cap and a tool base without a biasing element;

FIG. 9 is a side view of the non-biasing tooling system of FIG. 8 in anassembled state;

FIG. 9A is a cross-sectional view of the non-biasing tooling system ofFIG. 9;

FIG. 10 is a side view of a spar assembly cured in the non-biasingtooling system and illustrating a cool-down displacement occurring inthe spar assembly in the form of bowing along a spanwise direction as aresult of the dissimilar coefficients of thermal expansion of thecomposite D-spar and the metallic erosion strip;

FIG. 11 is an exploded side view of an embodiment of a tooling system asdisclosed herein having a biasing element fixedly attached to a lowerside of the tool base;

FIG. 11A is an exploded side view of the tooling system of FIG. 11;

FIG. 12 is a side view of a spar assembly being cured in the toolingsystem of FIG. 11-11A and illustrating a heat-up displacement in thecure tool when heated to a curing temperature due to the differencebetween the biasing element CTE and the cure tool CTE and causing thespar assembly to be cured in a distorted (e.g., bowed) shape;

FIG. 13 is a side view of the spar assembly removed from the toolingsystem after cool-down from the curing temperature and resulting in thespar assembly assuming a substantially straight or non-bowed shape alonga spanwise direction; and

FIG. 14 is a flow diagram illustrating one or more operations that maybe included in a method of manufacturing a composite article.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating preferred and various embodiments of the disclosure, shownin FIG. 1 is a perspective view of a spar assembly 202 for a rotor blade190 such as for a helicopter. The spar assembly 202 comprises acomposite article 170 containing at least two components 174 havingdifferent component coefficients of thermal expansion (CTEs) 176. Inthis regard, the spar assembly 202 may include a composite component 174comprising a composite D-spar 204 extending from a root 192 to a tip 194of the rotor blade 190 and which may have a swept tip portion 196. Thecomposite D-spar 204 may be formed as a composite layup 178 offiber-reinforced material having a composite layup coefficient ofthermal expansion (CTE) 180. The spar assembly 202 may further include ametallic component 182 comprising a metallic strip 186 having a metalliccomponent CTE 184. The metallic strip 186 may be adhesively bonded to aleading edge 200 of the composite D-spar 204 at an elevated curetemperature. Although the metallic strip 186 is shown extending from theroot 192 to the swept tip portion 196, the main rotor blade 190 may beconstructed such that the metallic strip 186 may terminate at anylocation such as at the tip 194.

FIG. 2 illustrates an embodiment of a tooling system 100 that mayadvantageously be used in a manufacturing process for manufacturing acomposite article 170 such as the spar assembly 202 illustrated in FIG.1 without significant shape distortion in the cured composite article172 (FIG. 1). For example, the tooling system 100 in FIG. 2 may be usedfor curing an adhesive 188 (FIG. 1) for bonding the metallic strip 186(FIG. 1) to the composite D-spar 204 at an elevated cure temperature.However, the tooling system 100 as disclosed herein may be configuredfor manufacturing composite articles 170 having any one of a variety ofdifferent sizes, shapes and configurations, without limitation, and isnot limited to manufacturing a spar assembly 202 of a rotor blade 190(FIG. 1).

Furthermore, the tooling system 100 and method disclosed herein is notlimited to the curing of adhesive 188 (FIG. 1) for bonding dissimilarcomponents 174. In this regard, the tooling system 100 as disclosedherein may be implemented for any type of elevated-temperatureprocessing of any type of composite article 170 comprised of two or morecomponents 174 (e.g., materials) having dissimilar component CTEs 176.For example, the tooling system 100 and method may be implemented forcuring a composite article 170 containing at least one uncured compositelayup 178 (FIG. 1) and/or for curing an adhesive 188 in a bondingoperation for bonding two components 174 having dissimilar componentCTEs 176. The tooling system 100 may also be implemented for co-curingoperations and/or for co-bonding operations at elevated processingtemperatures, or for any other type of processing elevated temperaturesin a composite article 170 comprising least two components 174 havingdifferent component CTEs 176.

For example, the tooling system 100 may be implemented for processing acomposite article 170 formed of composite components. Such compositecomponents may include composite layups 178 (FIG. 1) formed offiber-reinforced polymeric material such as a fiber-reinforcedthermoplastic matrix or a fiber-reinforced thermosetting matrix or resinsuch as an epoxy resin or any other type of resin. The thermoplasticresin or thermosetting resin may be reinforced with any one of a varietyof different types of fibers including, but not limited to, carbonfibers, glass fibers, aramid fibers, and other types of fibers. Thetooling system 100 may also be implemented for processing a compositearticle 170 containing metallic components, composite components, and/ornon-metallic components, or any combination thereof wherein at least twoof the components have dissimilar component CTEs 176.

In FIG. 2, the tooling system 100 may include a substantially rigidsupport frame 102 for supporting the cure tool 108 containing thecomposite article 170 to be cured. The cure tool 108 may include a curetool cavity 120 for containing the composite article 170 such as in anas-designed shape 160. The cure tool 108 may advantageously include abiasing element 130 that may be fixedly attached to the cure tool 108.Advantageously, the biasing element 130 may have a biasing element CTE134 that is different then the cure tool CTE 110. As described ingreater detail below, the biasing element 130 may be sized, configured,and positioned on the cure tool 108 such that the combination of thecure tool CTE 110 and the biasing element CTE 134 cause the cure tool108 to distort when the cure tool 108 and the composite article 170 areheated to a curing temperature. For example, the combination of the curetool CTE 110 and the biasing element CTE 134 may cause the cure tool 108to undergo a heat-up displacement 150 (FIG. 12) or shape change when thecure tool 108 and the composite article 170 are elevated to a curetemperature or other processing temperature. The composite article 170in the cure tool 108 may be cured in the distorted shape 162 (FIG. 12)such that when the composite article 170 is cooled from the curetemperature down to a reduced temperature such as ambient temperature orroom temperature, the cured composite article 172 (FIG. 1) may assume anas-designed shape 160 when unrestrained by the cure tool 108, asdescribed in greater detail below.

In FIGS. 2-3, the support frame 102 may include a plurality of braces104, 106 extending between the support frame 102 and the cure tool 108.The braces 104, 106 may be attached to the cure tool 108 and may begenerally vertically oriented and may be spaced apart from one another.One or more of the braces may comprise a fixed brace 104 and theremaining braces may be floating braces 106. For example, in FIGS. 2-3,one of the centrally located braces may be the fixed brace 104 and theremaining braces may be floating braces 106. The fixed brace 104 (e.g.,a non-floating brace) may be configured to non-movably secure a point ofthe cure tool 108 to the support frame 102 to prevent movement of thecure tool 108 relative to the support frame 102 at that location on thecure tool 108. One or more floating braces 106 may be configured toallow the cure tool 108 and biasing element 130 to move in the heat-updisplacement 150 (FIG. 12) direction 154 (FIG. 12) while restrainingmovement of the cure tool 108 in other directions such as twistingmovement, lateral movement, or any other movement of the cure tool 108that is not in the direction 154 of the heat-up displacement 150.

Referring to FIG. 4, shown is a cross section of the tooling system 100illustrating the cure tool 108 supported by braces 104, 106 extendingupwardly from the support frame 102. At the location of thecross-section in FIG. 4, the cure tool 108 is shown orientednon-vertically which may illustrate a spanwise blade twist that may bedesigned into the spar assembly 202 (FIG. 5) of the rotor blade 190(FIG. 5). The support frame 102 may be configured as a relatively rigidstructure configured to provide relatively high torsional stiffness andhigh bending stiffness to the support frame 102. The high torsionalstiffness and bending stiffness of the support frame 102 may restrict orlimit movement of the cure tool 108 and biasing element 130 to movementcorresponding to the heat-up displacement 150 (FIG. 12). In this regard,the support frame 102 may be configured to substantially prevent orminimize movement of the cure tool 108 such as unwanted twistingmovement or lateral movement of the cure tool 108 which the compositearticle 170 may otherwise undesirably assume during curing at anelevated cure temperature.

In the context of curing a spar assembly 202 (FIG. 5) for a rotor blade190 (FIG. 5) as described herein, the heat-up displacement 150 (FIG. 12)of the cure tool 108 and the biasing element 130 may includethermally-induced bowing 164 (FIG. 12) of the cure tool 108 and biasingelement 130 into the distorted shape 162 when heated as mentioned above.The support frame 102 and the braces 104, 106 may be configured toprevent twisting or lateral movement of the cure tool 108. The supportframe 102 and the braces 104, 106 may be configured to allow the curetool 108 and the biasing element 130 to thermally expand under heatingto facilitate bowing 164 of the cure tool 108 into the distorted shape162 (FIG. 2), such that upon cool down, the cured composite article 172(FIG. 1) assumes the as-designed shape 160 wherein the cured compositearticle 172 is substantially straight. The change from the distortedshape 162 at the cure temperature to the as-designed shape 160 atambient temperature (e.g., room temperature) is a result ofthermally-induced mechanical stress occurring in the cured compositearticle 172 during cool down due to the dissimilar components CTEs 176of the cured composite article 172.

As may be appreciated, the cure tool 108 and biasing element 130 may beconfigured in any one of a variety of different shapes, sizes, andconfigurations to facilitate any type or direction 154 of heat-updisplacement 150 in the cure tool 108, and is not limited to heat-updisplacement 150 of the cure tool 108 into a bowed shape (FIG. 12). Inthis regard, the cure tool 108 and the biasing element 130 may beconfigured such that the heat-up displacement 150 results inmulti-dimensional heat-up displacement 150 wherein the cure tool 108distorts into a complex curvature shape, and is not limited toessentially one-dimensional heat-up displacement 150 such as theone-dimensional bowing of the spar assembly 202 (FIG. 5) as disclosedherein. Furthermore, the cure tool 108 and the biasing element 130 maybe configured to cause non-linear heat-up displacement 150 in the curetool 108 at the elevated cure temperature or processing temperature, asdescribed in greater detail below.

In FIG. 4, in an embodiment, the biasing element 130 may be formed ofmetallic material such as titanium or other metallic or non-metallicmaterial. The cure tool 108 may be formed of Invar, steel or otheralloys. The cure tool 108 may also be formed of composite material orother non-metallic material. The biasing element 130 may be formed ofany material having a biasing element CTE 134 that is different than thecure tool CTE 110. In the embodiment shown, the biasing element 130 maybe fixedly attached to a lower side of the cure tool 108. For example,the biasing element 130 may be fixedly attached to the cure tool 108 atan interface 144 there between. The tooling system 100 may includecutouts in the braces 104, 106 (FIG. 3) such that the braces 104, 106are disposed in non-contacting relation to the biasing element 130 toallow unrestricted thermal expansion and contraction of the biasingelement 130 during heating and cooling. Alternatively, each bracelocation on the cure tool 108 may include separate braces 104, 106 onopposite sides of the biasing element 130 and wherein the braces 104,106 are disposed in non-contacting relation to the biasing element 130to allow for unrestricted thermal expansion and contraction thereofduring heating and cooling.

In FIG. 4, the biasing element 130 may comprise a substantially rigidmember formed of any suitable metallic material and/or non-metallicmaterial and wherein the biasing element 130 has a biasing element CTE134 that is different than the cure tool CTE 110. For example, thebiasing element CTE 134 may be lower or higher than the cure tool CTE110 in order to effectuate a desired direction 154 (FIG. 12) of theheat-up displacement 150 (FIG. 12) of the cure tool 108 into thedistorted shape 162 (FIG. 2). In the embodiment shown, the biasingelement 130 may be fixedly attached to the cure tool 108. For example,the biasing element 130 may be mechanically fastened, wedded, orotherwise attached to the cure tool 108 in a manner preventing relativemovement between the biasing element 130 and the cure tool 108, at leastin a lengthwise direction 112 (FIG. 3) of the cure tool 108. In thismanner, the thermal expansion and contraction of the biasing may bedirectly imparted to the cure tool 108. However, it is contemplated thatthe biasing element 130 may be attached to the cure tool 108 in a mannerpreventing relative movement therebetween, at least along a direction154 corresponding to the heat-up displacement 150, and may be floatingin a manner allowing relative movement in directions not associated withthe heat-up displacement 150.

Referring to FIG. 5, shown is a perspective view of the cure tool 108and the biasing element 130 with the support frame and braces omittedfor clarity. The biasing element 130 may extend from a root 192 end ofthe cure tool 108 to a location of the swapped tip 194 portion of thecomposite article 170. However, the biasing element 130 may beconfigured to extend along any length or portion of the cure tool 108and is not limited to extending along an entire length of the cure tool108. Furthermore, the biasing element 130 may be configured as anon-continuous member in order to achieve a desired distorted shape 162(FIG. 2) in the cure tool 108 when elevated to the cure temperature orother processing temperature. In the embodiment shown, the biasingelement 130 may be provided in a biasing element length 142 (FIG. 6) andhaving a biasing element cross section 136 of any size, shape andconfiguration, without limitation, to achieve a desired distorted shapein the cured composite article 172 (FIG. 1) prior to cool down.

Referring to FIG. 6, shown is an exploded view of the cure tool 108, thebiasing element 130, and the spar assembly 202. In the embodiment shown,the biasing element 130 may be provided in a biasing element length 142that extends along a lengthwise direction 112 of the cure tool 108. Thebiasing element 130 may have a biasing element cross section 136 of anysize, shape and configuration, without limitation. In this regard, thebiasing element 130 is not limited to the generally rectangular shape ofthe biasing element cross section 136 shown in FIG. 6.

In FIG. 6, the metallic strip 186 (e.g., erosion strep) is shown priorto installation onto the leading edge 200 of the composite D-spar 204and prior to loading the assembled the metallic strip 186 and compositeD-spar 204 into the cure tool cavity 120. The cure tool 108 cap mayextend along a length of the cure tool 108 and may be configured toenclose the cure tool cavity 120 for containing the composite article170 (e.g., the spar assembly 202) to be cured. It should be noted thatalthough the cure tool 108 as disclosed herein includes a female curetool cavity 120 enclosed by the tool cap 124, the cure tool 108 may beprovided in any configuration including a male cure tool configuration(not shown) wherein a composite article such as a composite layup may beapplied over the male cure tool. The cure tool 108 may be provided inany size, shape and configuration and may include a biasing element 130fixedly attached thereto and having a biasing element CTE 134 (FIG. 5)that is different than the cure tool CTE 110 in order to cause a heat-updisplacement 150 (FIG. 12) in the composite article 170 that results inthe cured composite article 172 (FIG. 1) assuming an as-designed shape160 upon cool down from the curing temperature.

Referring to FIG. 7, shown is an exploded view of the tooling system 100including the tool cap 124, the cure tool 108, and the biasing element130. Also shown is the spar assembly 202 including the metallic strip186 which may be applied to the composite D-spar 204 and loaded into acure tool cavity 120 for curing the adhesive 188 for bonding themetallic strip 186 to the composite D-spar 204. The cure tool cavity 120may be defined by the mold portion 116 and the tool cap 124. The toolbase 114 may include a pair of base flanges 118 extending laterallyoutwardly from the mold portion 116. The tool cap 124 may include a capportion 126 and a pair of cap flanges 128 extending laterally outwardlyfrom the cap portion 126. The cap flanges 128 may be receivable within acorresponding pair of recesses 122 that may be formed in the baseflanges 118 for maintaining the cap portion 126 in registration with themold portion 116. The tool cap 124 may be configured to be removablymateable to the tool base 114. The cap portion 126 and the mold portion116 may collectively define or enclose the cure tool cavity 120.

In FIG. 7, the biasing element 130 is shown having a biasing elementcross section 136 with a rectangular shape having a biasing elementwidth 140 and a biasing element height 138. However, the biasing elementcross section 136 may be provided in any shape and size and is notlimited to a rectangular shape. Further in this regard, the biasingelement cross section 136 may vary along a length of the cure tool 108.For example, in order to achieve a non-linear distortion of the curetool 108 during heating to the elevated cure temperature, the biasingelement cross section 136 area may be varied by varying the biasingelement width 140, biasing element height 138, and/or biasing elementshape.

The biasing element 130 is shown mounted on an underside of the toolbase 114. Due to the biasing element CTE 134 being different than thecure tool CTE 110, the thermal expansion of the biasing element 130 in alengthwise direction 112 causes the cure tool 108 and biasing element130 to undergo a heat-up displacement 150 (FIG. 12) during which thecure tool 108 and biasing element 130 assume a bowed, distorted shape162 (FIG. 2). As may be appreciated, the biasing element 130 may befixedly attached to the cure tool 108 at a location on the cure tool 108such that the heat-up displacement 150 is substantially opposite indirection 154 (FIG. 12) and substantially equivalent in magnitude 152(FIG. 12) to a cool-down displacement 350 (FIG. 10) of a cured compositearticle 370 (FIG. 10) cured on a non-biasing cure tool 302 (FIGS. 9-9A)as described in greater detail below.

Referring to FIGS. 8-8A, shown are exploded perspective and sectionalviews of a non-biasing tooling system 300 that is configured similar tothe tooling system 100 shown in FIGS. 2-7 with the exception that thenon-biasing tooling system 300 lacks a biasing element 130. Thenon-biasing tooling system 300 is disclosed herein to illustrate thecool-down displacement 350 (FIG. 10) that occurs when a compositearticle 170 is cured in a generally non-distorted shape 162 (FIG. 2) atan elevated cure temperature and which then distorts upon cool down toambient temperature. In FIGS. 8-8A, the non-biasing tooling system 300includes a non-biasing cure tool 302 having a lengthwise direction 304.The non-biasing cure tool 302 may include a tool base 306 having a moldportion 308 and a pair of base flanges 310. They may include a tool cap124 (FIG. 7) having a cap portion 126 (FIG. 7) and a pair of cap flanges128 (FIG. 7) to engage the base flanges 310. The composite article 170cured in the non-biasing tooling system 300 may have substantially thesame configuration as the tooling system 100 shown in FIGS. 2-7.

Referring to FIGS. 9-9A, shown are views of the non-biasing toolingsystem 300 of FIG. 8-8A in an assembled state. The composite article 170(FIG. 8) may be loaded into the cure tool cavity 312 of the tool base314. The temperature of the non-biasing tooling system 300 may beelevated to a cure temperature. Upon heating of the non-biasing toolingsystem 300 to the elevated cure temperature, the tool base 314 and toolcap 316 may thermally expand in a generally non-bowed shape or astraight shape.

Referring to FIG. 10, shown is a side view of a cured spar assembly 202that may be cured in the non-biasing tooling system 300 illustrated inFIGS. 8-9A. FIG. 10 illustrates a cool-down displacement 350 that mayoccur during cooling of the cured spar assembly 202 in the form ofbowing 164 along a spanwise direction 198 of the cured spar assembly202. The cured spar assembly 202 has a cool-down displacement 350magnitude 352 and direction 354. The bowing 356 in the cured sparassembly 202 may occur as a result of the dissimilar CTEs of themetallic strip 186 and the composite D-spar 204. In this regard, thecooling of the cured spar assembly 202 represents the response of acured composite article 172 (FIG. 1) to thermally-induced mechanicalstress imbalance in the cured composite article 172 due to thedissimilar component CTEs 176.

Referring to FIGS. 11-11A, shown are exploded perspective and sectionalviews of the tooling system 100 illustrated in FIGS. 2-7. The toolingsystem 100 advantageously includes the biasing element 130 fixedlyattached to the tool base 114. As described above, the biasing element130 may be attached to a side of the cure tool 108 (e.g., a lower side)that is located opposite the cool-down displacement 350 direction (FIG.10) of the cured composite article 370 (FIG. 10) that is cured on thenon-biasing tooling system 300 shown in FIGS. 8-9A.

Referring to FIG. 12, shown is a side view of the tooling system 100 atthe elevated cure temperature and illustrating a heat-up displacement150 in the cure tool 108 when heated to a curing temperature. Asindicated above, the tooling system 100 may assume a distorted shape 162(e.g., a bowed shape) corresponding to the heat-up displacement 150 as aresult of the biasing element CTE 134 being different than the cure toolCTE 110. In an embodiment, the biasing element 130 may have a biasingelement CTE 134 and a biasing element cross section 136 that results inthe magnitude 152 of the heat-up displacement 150 of the cure tool 108being substantially equivalent to the magnitude 352 (FIG. 10) of thecool-down displacement 350 (FIG. 10) of the cured spar assembly 202using the non-biasing tooling system 300 shown in FIG. 8-9A.

Referring to FIG. 13, shown is the cured spar assembly 202 removed fromthe tooling system 100 (FIG. 12) after cool-down from the elevatedcuring temperature. Due to thermally-induced stress imbalance in thecured spar assembly 202 caused by the difference in the CTE of themetallic strip 186 relative to the CTE of the composite D-spar 204, thecured spar assembly 202 may assume the as-designed shape 160 which mayadvantageously comprise a generally straight or non-bowed shape of thespar assembly 202 along a spanwise direction 198.

Referring to FIG. 14, shown is a flow diagram illustrating one or moreoperations that may be included in a method 400 of manufacturing a curedcomposite article 172 (FIG. 1). Advantageously, the method provides ameans for exploiting the thermally-induced mechanical stress imbalanceoccurring in a composite article 170 (FIG. 1) formed of components 174(FIG. 1) having differing component CTEs 176 (FIG. 1).

Step 402 of the method 400 of FIG. 14 may include providing a cure tool108 (FIG. 3) having a biasing element 130 (FIG. 3) fixedly attachedthereto. As was indicated above, the biasing element 130 may have abiasing element CTE 134 (FIG. 3) that is different than the cure toolCTE 110 (FIG. 3). For example, the biasing element CTE 134 may be higheror lower than the cure tool CTE 110. In FIGS. 2-8, the biasing element130 has a constant cross section 136 shape and size along the length ofthe biasing element 130. For a cure tool 108 having a generally constantcross section 136 shape and size, the biasing element 130 configurationshown in FIGS. 2-8 may result in linear displacement of the cure tool108 along a lengthwise direction 112 of the cure tool 108.

However, the cure tool 108 (FIG. 7) may be provided in an embodimentwherein the biasing element 130 (FIG. 7) has at least one biasingelement parameter 132 (FIG. 7) that varies linearly or non-linearlyalong a length of the cure tool 108. Examples of biasing elementparameters 132 that may be varied along a length of the cure tool 108include, but are not limited to, the biasing element CTE 134, thebiasing element cross section 136 (FIG. 7), and/or the biasing element130 stiffness or Young's modulus. The biasing element cross section 136may include the cross-section size and/or the cross-section shape. Forexample, in FIG. 7, the biasing element 130 includes a generallyrectangular cross section having a biasing element width 140 and abiasing element height 138. The biasing element width 140 and/or thebiasing element height 138 may be varied along a length of the biasingelement 130 to vary the cross section area of the biasing element 130and achieve a non-linear heat-up displacement 150 (FIG. 12) in the curetool 108. The biasing element cross-section 136 shape may also be variedalong a length of the biasing element 130. For example, the biasingelement 130 may be provided in a cross section that changes from arectangular shape to a different cross section shape such as an I-beamshape or any other shape in order to cause the cure tool 108 to distortinto a specific distorted shape 162 (FIG. 12).

The biasing element parameters 132 (FIG. 6) may be varied non-linearlyalong the length of the cure tool 108 (FIG. 6) to cause a heat-updisplacement 150 (FIG. 12) in the cure tool 108 that is non-linear atthe processing temperature. In this manner, the composite article 170(FIG. 6) may cure in a specific distorted shape 162 (FIG. 12) thatresults in the cured composite article 172 (FIG. 11) assuming a specificas-designed shape 160 (FIG. 13) upon cool down to ambient temperature.For example, one or more of the biasing element parameters 132 may bevaried non-linearly along a length of the cure tool 108 to correspond tonon-linear thermally induced stress in the cured composite article 172(FIG. 11) as may result from a tapered thickness in the metallic strip186 (FIG. 6) along a length of the spar assembly 202 (FIG. 6).

Further in this regard, the tooling system 100 may include two or moreindividual biasing elements 130 (FIG. 6) that may be fixedly attached tothe tool base 114 (FIG. 6). The biasing elements 130 may have dissimilarbiasing element parameters 132. For example, two or more individualbiasing elements 130 formed of different materials having dissimilarCTEs may be joined end-to-end and fixedly attached to the tool base 114.Upon heating the cure tool 108 (FIG. 6) and the biasing elements 130 tothe designated curing temperature or processing temperature, anon-linear heat-up displacement 150 (FIG. 12) may be generated in thecure tool 108 to correspond to non-linear cool-down displacement 350(FIG. 10) that may occur in a cured composite article 172 (FIG. 13) as aresult of non-linear geometric of mechanical properties of one or moreof the components of the composite article 172. For example, themetallic strip 186 (FIG. 6) of the spar assembly 202 (FIG. 6) may have atapered thickness along a length of the D-spar 204 (FIG. 6).

Step 404 of the method 400 of FIG. 14 may include loading a compositearticle 170 (FIG. 6) on or in the cure tool 108 (FIG. 6). The compositearticle 170 may be comprised of two or more components 174 (FIG. 6)having dissimilar component CTEs 176 (FIG. 6). For example, in FIG. 6,the metallic strip 186 of the spar assembly 202 may have a metalliccomponent CTE 184 that is different that the composite component CTE 176of the composite D-spar 204. However, the composite article 170 mayinclude components 174 formed of any material, without limitation. Forexample, one or more of the composite articles 170 may comprise anuncured composite layup, a pre-cured composite layup, a metalliccomponent, an adhesive, or any of the type of metallic component ornon-metallic component, without limitation.

Step 406 of the method 400 of FIG. 14 may include heating the compositearticle 170 (FIG. 7) and the cure tool 108 (FIG. 7) to an elevatedcuring temperature. In this regard, the composite article 170 may beloaded onto or in the cure tool 108 at ambient temperature or roomtemperature or other temperature. The cure tool 108 may then bepositioned inside an autoclave (not shown) and the temperature may beelevated to the designated cure temperature required for curing adhesive188 (FIG. 7) for bonding the metallic strip 186 (FIG. 7) to thecomposite D-spar 204 (FIG. 7). However, the cure tool 108 and compositearticle 170 may be heated by any means and are not limited to heatingusing an autoclave.

Furthermore, the cure tool 108 (FIG. 7) in composite article 170 (FIG.7) may be heated to any temperature and are not limited to heating tothe cure temperature of an adhesive 188 (FIG. 7) or the cure temperatureof a composite layup 178 (FIG. 7). For example, the cure tool 108 andthe biasing element 130 (FIG. 7) may be elevated to a temperature thatis higher than the curing temperature of an adhesive 188 or a compositelayup 178, and which may effectuate an increased amount of heat-updisplacement 150 (FIG. 12) in the cure tool 108. By causing an increasedamount of heat-up displacement 150 in the cure tool 108, the curedcomposite article 172 (FIG. 7) may undergo an increased amount of shapechange upon cool down to ambient temperature.

Step 408 of the method 400 of FIG. 14 may include distorting the curetool 108 (FIG. 12) and the composite article 170 (FIG. 12) into adistorted shape 162 (FIG. 12) associated with a heat-up displacement 150(FIG. 12) in response to elevating the temperature of the cure tool 108to the curing temperature. The distortion may occur in the cure tool 108as a result of the difference in the cure tool CTE 110 (FIG. 12)relative to the biasing element CTE 134. For example, FIG. 12illustrates the cure tool 108 distorting into a bowed shape along alengthwise direction 112 when heated to the curing temperature.

Step 410 of the method 400 of FIG. 14 may include curing the compositearticle 170 (FIG. 12) in the distorted shape 162 (FIG. 12). In FIG. 12,when the composite article 170 is at the curing temperature, theadhesive 188 between the metallic strip 186 and the composite D-spar 204may cure. In an embodiment, the composite article 170 may include anuncured composite layup 178 (e.g., prepreg composite plies) having aresin matrix that may cure (e.g., for thermosetting resin) when held ata designated curing temperature for a designated period of time, and/orsolidify (e.g., for thermoplastic resin) when cooled to a temperaturebelow a glass transition temperature of the thermoplastic resin.

Step 412 of the method 400 of FIG. 14 may include cooling the curedcomposite article 172 (e.g., to ambient temperature) (FIG. 13) such thatthe cured composite article 172 changes shape from the distorted shape162 (e.g., at the cured temperature) (FIG. 12) to an as-designed shape160 (e.g., at ambient temperature) when the cured composite article 172(FIG. 13) is removed from the cure tool 108 (FIG. 12) or the curedcomposite article 172 is otherwise unrestrained. For example, FIG. 13illustrates the cured spar assembly 202 substantially straightening outwhen cooled to a reduced temperature (e.g., ambient temperature) due tothe thermally-induced stress caused by the dissimilar CTEs of themetallic strip 186 and the composite D-spar 204.

In an embodiment, the method disclosed herein may include forming, usingthe tooling system 100 (FIG. 7), a helicopter rotor blade 190 (FIG. 7)from any type of component such as from one or more uncured or pre-curedcomposite layup 178 (e.g., a composite D-spar 204) and any metalliccomponents such as a metallic strip 186 (FIG. 7) that may be laminatedwith the composite layup 178. However, the tooling system 100 may beimplemented for forming any one of a variety of different compositearticles 170 (FIG. 7) having two or more components 174 (FIG. 7) withdissimilar component CTEs 176 (FIG. 7), and is not limited to forming arotor blade 190.

In an embodiment not shown, the cure tool 108 and biasing element 130may be configured such that after heating the cure tool 108 and thebiasing element 130 to an elevated temperature to cause a heat-updisplacement 150 and allowing the composite article 170 to cure, thecured composite article 172 undergoes a shape change into a finalas-designed shape that may be a curved shape. For example, although notshown in the figures, a cure tool 108 and biasing element 130 may beinitially configured to hold the uncured composite article 170 in acurved shape prior to heating. The cure tool 108 and the biasing element130 may be heated to an elevated cure temperature causing the cure tool108 and the biasing element 130 to undergo a heat-up displacement into adistorted shape such as a straight shape. Upon cool down such as toambient temperature, the cured composite article 172 may assume a curvedshape.

Additional modifications and improvements of the present disclosure maybe apparent to those of ordinary skill in the art. Thus, the particularcombination of parts described and illustrated herein is intended torepresent only certain embodiments of the present disclosure and is notintended to serve as limitations of alternative embodiments or deviceswithin the spirit and scope of the disclosure.

What is claimed is:
 1. A tooling system, comprising: a cure tool havinga cure tool coefficient of thermal expansion (CTE) and configured forcuring a composite article formed of two or more components havingdissimilar component CTEs; a biasing element fixedly attached to thecure tool along a lengthwise direction of the cure tool in a mannerpreventing relative movement between the biasing element and the curetool along the lengthwise direction, the biasing element having abiasing element CTE that is different than the cure tool CTE; and thebiasing element being configured such that a combination of the curetool CTE and the biasing element CTE causes a heat-up displacement ofthe cure tool and biasing element along a direction non-parallel to thelengthwise direction when the cure tool and biasing element are heatedand the composite article is cured in a distorted shape on the heatedcure tool such that when cooled, the cured composite articlesubstantially assumes an as-designed shape due to the dissimilarcomponent CTEs of the composite article.
 2. The tooling system of claim1, wherein: the biasing element is fixedly attached to the cure tool ata location such that the heat-up displacement is substantially oppositein direction to a cool-down displacement of a cured composite articlecured on a non-biasing cure tool.
 3. The tooling system of claim 1,wherein: the biasing element is configured such that the heat-updisplacement is substantially equivalent in magnitude to the cool-downdisplacement of a cured composite article cured on a non-biasing curetool.
 4. The tooling system of claim 1 wherein: the heat-up displacementcomprises bowing along the lengthwise direction of the cure tool.
 5. Thetooling system of claim 1 wherein: the heat-up displacement comprisestwisting of the cure tool along the lengthwise direction.
 6. The toolingsystem of claim 1 wherein: the biasing element has at least one biasingelement parameter that varies along a length of the cure tool, thebiasing element parameter including at least one of the following: thebiasing element CTE; a biasing element cross section; and a biasingelement stiffness.
 7. The tooling system of claim 6 wherein: the biasingelement parameter varies non-linearly along the lengthwise direction ofthe cure tool.
 8. The tooling system of claim 6 wherein: the biasingelement comprises at least two biasing elements having dissimilarbiasing element parameters; and the biasing elements being configured togenerate non-linear heat-up displacement in the cure tool.
 9. Thetooling system of claim 1 further comprising: a support frame forsupporting the cure tool and configured to limit movement of the curetool to a direction associated with the heat-up displacement.
 10. Thetooling system of claim 9 wherein: the cure tool is fixedly secured tothe support frame at one location on the support frame in such a mannerpreventing movement of the cure tool relative to the support frame atthe one location; and the cure tool being non-movably secured to thesupport frame at one or more remaining locations on the support frame insuch a manner allowing the cure tool and the biasing element to movealong a direction of the heat-up displacement at the remaininglocations.
 11. The tooling system of claim 1 wherein: the cure tool andthe biasing element are configured such that the heat-up displacement isone-dimensional heat-up displacement.
 12. The tooling system of claim 1wherein: the cure tool and the biasing element are configured such thatthe heat-up displacement is multi-dimensional heat-up displacementduring which the cure tool distorts into a complex curvature shape. 13.The tooling system of claim 1 wherein: the components of the compositearticle include a composite layup having a composite layup CTE, and ametallic component having a metallic component CTE that is differentthan the composite layup CTE.
 14. The tooling system of claim 1 wherein:the cure tool is configured to cure a spar assembly of a rotor blade.15. The tooling system of claim 1 wherein: at least one of the cure tooland the biasing element is formed of metallic material and/ornon-metallic material.
 16. The tooling system of claim 15 wherein: themetallic material comprises at least one of steel, titanium, Invar; andthe non-metallic material comprises ceramic material and compositematerial including fiber-reinforced polymeric material.
 17. A toolingsystem for a composite assembly, comprising: a cure tool having a curetool coefficient of thermal expansion (CTE) and configured for curing acomposite article formed of two or more components having dissimilarcomponent CTEs; a biasing element fixedly attached to the cure toolalong a lengthwise direction of the cure tool in a manner preventingrelative movement between the biasing element and the cure tool alongthe lengthwise direction, the biasing element having a biasing elementCTE that is different than the cure tool CTE; the biasing element beingconfigured such that a combination of the cure tool CTE and the biasingelement CTE causes a heat-up displacement of the cure tool and biasingelement along a direction non-parallel to the lengthwise direction whenthe cure tool and biasing element are heated to a cure temperature andthe composite article is cured in a distorted shape on the heated curetool such that when cooled to ambient temperature, the cured compositearticle substantially assumes an as-designed shape when unrestrained dueto the dissimilar component CTEs of the composite article; and thebiasing element being fixedly attached to the cure tool at a locationsuch that the heat-up displacement of the cure tool is substantiallyopposite in direction to a cool-down displacement of a composite articlecured on a non-biasing cure tool.
 18. The tooling system of claim 17wherein: the heat-up displacement is substantially equivalent inmagnitude to a cool-down displacement of a cured composite article curedon a non-biasing cure tool.
 19. A tooling system for curing a compositespar assembly of a helicopter rotor blade, comprising: a cure toolhaving a cure tool cavity configured to receive a composite sparassembly of a rotor blade having a composite layup coefficient ofthermal expansion (CTE) and a metallic strip CTE that is different thanthe composite layup CTE, the cure tool having a cure tool CTE; a biasingelement fixedly attached to the cure tool along a lengthwise directionof the cure tool in a manner preventing relative movement between thebiasing element and the cure tool along the lengthwise direction, thebiasing element having a biasing element CTE that is different than thecure tool CTE; and the biasing element being configured such that acombination of the cure tool CTE and the biasing element CTE causes aheat-up displacement of the cure tool and biasing element along adirection non-parallel to the lengthwise direction when the cure tooland biasing element are heated and the composite spar assembly is curedin a distorted shape on the heated cure tool such that when cooled, thecured composite spar assembly substantially assumes an as-designed shapedue to the metallic strip CTE being different than the composite layupCTE of the composite spar assembly.
 20. The tooling system of claim 19wherein: the cure tool has a tool base and a tool cap collectivelydefining the cure tool cavity configured to contain the composite sparassembly; and the tool cap being removably mateable to the tool base forloading and removing the composite spar assembly from the cure toolcavity.